This isn’t the first time Megan has bounced back from pregnancy in record time.

In 2012, Fox lost all her baby weight just two months after giving birth to her first son, Noah. Megan gained just 23 pounds during her first pregnancy and lost the weight quickly by following the dairy-free Paleo diet.

Paleo Diet Is Twice as Effective for Weight Loss

The Paleo diet has a large celebrity following, including Tim McGraw (who credits it for his eye-popping 40-pound weight loss), Joe Manganiello, and supermodel Adriana Lima.

A recent study published in the European Journal of Clinical Nutrition indicates the Paleo diet is twice as effective as other diets for promoting weight loss and reducing belly fat.

The two-year study tracked 70 overweight, post-menopausal women who were assigned either a low-fat diet or a low-carb (higher-fat) Paleo diet. Study participants were measured for weight, cholesterol and blood sugars after six months on their respective diets, and again after two years. The results showed the Paleo dieters lost significantly more weight (14 pounds) compared to the low-fat dieters (5.7 pounds).

What’s more, the low-carb, high-fat Paleo dieters lost 4 inches from their waists after six months, compared to just 2 inches for the low-fat dieters. In previous studies, the Paleo diet has routinely beaten low fat diets at controlling cholesterol and diabetes.

The results are noteworthy because older women — especially those who are post-menopausal — have historically reported having a hard time losing weight, especially from their mid-sections, due to slower metabolisms and hormone disruptions.

“The Paleo diet is the healthiest way you can eat because it is the only nutritional approach that works with your genetics to help you stay lean, strong and energetic,” said fitness expert Robb Wolf, author of The Paleo Solution: The Original Human Diet.

Studies shows the Paleo diet works well for women because it reduces the blood sugar spikes and hormone surges that fuel overeating, mood swings and weight gain, said Nell Stephenson, author of Paleoista: Gain Energy, Get Lean.

Worked Out During Pregnancy

Fox’s longtime trainer, Harley Pasternak, credited Megan’s workouts during her pregnancy for her speedy post-baby weight loss. “We worked out throughout her entire pregnancy,” Harley told People. “She was a model of health through the whole process.”

Fox’s workouts combine cardio exercise with strength-training and stretching. While Fox often downplays the efforts she takes to stay fit, she’s actually quite conscientious when it comes to diet and exercise.

“Megan really educated herself big-time and had a great relationship with her physician so she really understood the safe boundaries of how to exercise and eat well during pregnancy,” said Pasternak, who has trained Halle Berry, Lady Gaga, and Jessica Simpson.

Fox and her husband, actor Brian Austin Green, both make a healthy diet a top priority. “Megan and Brian eat really well,” said Pasternak, author of The Body Reset Diet.

“They both cook and love using their blender. Megan’s favorite is the red smoothie, which is whatever berries are in season, Chai tea, a scoop of protein powder and little bit of almond milk.”